Visual attention enables the processing of relevant stimuli while minimizing interference from irrelevant and potentially distracting events. Research in attention aims to understand its effects upon specific stages of information processing and its contributions to perception and behavior. Models of spatial attention have emphasized (i) the role of attention in resolving competitive interactions among stimuli for processing resources, (ii) the allocation of attentional resources to locations and objects in the visual scene, and (iii) the distinction between voluntary and reflexive attentional orienting. Psychophysical paradigms using response time and signal detection measures isolate information processing components and provide indices of attention effects at different processing stages. Physiological paradigms using event related potentials (ERPs) provide parallel measures of the neural activity related to discrete stages of stimulus processing, as well as that related to executive control mechanisms. Neuroimaging using functional magnetic resonance imaging (fMRI) can be employed to aid in the localization of the effects of attention to specific visual areas, as well as in the determination of the neuroanatomical circuitry that mediates the control of attention. This proposal has four aims: (1) to investigate the mechanisms of spatial attention in (a) modulating incoming signals at early stages of visual cortical processing, (b) reducing competitive interactions among stimuli in multiple visual areas, and (c) biasing visual cortex activity ("priming") via top-down control processes, (2) to investigate the neural mechanisms of space versus feature and object-based attention, (3) to investigate the neural systems and circuits that mediate voluntary attentional orienting and re-orienting, and (4) to investigate the neural mechanisms of social attention (orienting to the direction of another?s gaze-i.e., gaze orienting). Throughout the proposed research, the relation between psychophysical and physiological measures will be emphasized in order to provide direct links between psychophysically defined properties of spatial attention and the underlying neural mechanisms. Further, the combined use of ERPs and fMRI will provide complementary measures of the time course and functional anatomy of attentional mechanisms. Because selective attention is an essential cognitive process, elucidating basic attention mechanisms in humans remains a high priority in the effort to understand, diagnose and treat neurological conditions that involve deficits in attention.